In the personal care industry, particularly with respect to personal care products for skin, there is a need for ingredients that provide coverage for age spots, blemishes, discolorations, etc., as well as provide a natural look. It is a well known problem that cosmetic products that provide good coverage have a mask-like, unnatural appearance. This is particularly true with titanium dioxide-based materials, the most common type of opacifiers found in cosmetics. Many cosmetic compositions have been reported that provide high coverage with some degree of “naturalness”, however none have provided the level of naturalness that is highly desired by consumers without sacrificing the required coverage.
Examples of hollow particles have been previously described. However, previously described materials have significant shortcomings as potential opacifiers in cosmetic formulations. Co- and terpolymer systems made from vinylidene chloride and acrylonitrile, or from vinylidene chloride, acrylonitrile and methylmethacrylate have been reported (e.g. Expancel™). Unfortunately these types of materials are only readily available in particle sizes that exceed the sizes believed necessary to achieve maximum optical performance benefits in cosmetic uses. Styrene/acrylate hollow particles (e.g. Ropaque™, Rohm & Haas) are also known, however these particles do not provide the desired optical benefits in cosmetic formulations.
Hollow particles with polymer shells can be made by creating core/shell particles containing a core with hydrolyzable acid groups and a sheath, or shell, that is permeable to a base. Hollow particles with silica shells synthesized using a layer-by-layer electrostatic deposition technique on a template are also known. In addition, hollow particles have also been synthesized by depositing nanoparticles derived from alkoxysilanes on a template particle, as well as by condensation of sodium silicate on a template particle followed by template removal. However, such particles often show a lack of continuity in the particle surface and thus often exhibit unacceptable shell permeability. Further, none of the known and reported particles have been made according to a method that allows for creation of the particles in a desired, substantially uniform, narrow range with narrow particle size distributions and having acceptable permeability, or they otherwise involve numerous synthetic steps which make their production impractical for use in personal care applications.